Thanks for your response. Do you mean that my gallery won't work at all with WP Super Cache?

I have read that google can index those urls, but for some reason it doesn't for my website. Other pages get indexed very quick, but my gallery pages are not. It is a bit frustrating ;-)

I have tried some things to improve, for example changing the alt and adding title tags for the photos to a meaningful title. The Aniga plugin used to show the filename with the alt tag. But no improvements :-(

I am thinking about modifying the plugin more, so I can use static links instead of dynamic ones. Although I am not sure how to do this, so it will require a lot of experimenting on my part.
Another option could be changing to the gallery option in the new WP versions. I have tried this, but I guess I have to change my templates for this to work properly.

Maybe there are some other options I could try. Please let me know if I have overlooked something. Tips are highly appreciated :-)